Transfer method for manufacturing conductor structures by means of nano-inks

ABSTRACT

A method for equipping a film material with at least one electrically conductive conductor structure, wherein a dispersion containing metallic nanoparticles in the form of a conductor structure is applied to a thermostable transfer material and the metallic nanoparticles are sintered to form an electrically conductive conductor structure. The electrically conductive conductor structure of sintered metallic nanoparticles is then transferred from the thermostable transfer material to the non-thermostable film material. A method for producing a laminate material using the film material using at least one electrically conductive conductor structure, and to the corresponding film material and laminate material are described.

BACKGROUND OF THE INVENTION

A. Field of the Invention

The subject matter of the present invention is a method for equipping afoil material with at least one electrically conductive conductorstructure, a method for manufacturing a laminate material which has atleast two layers made of foil material and at least one electricallyconductive conductor structure between the layers made of foil material,as well as foil materials manufactured by means of the method accordingto the invention and laminate materials having at least one electricallyconductive conductor structure. Subject matter of the present inventionare also products manufactured with the foil material and laminatematerial of the invention, such as for example security documents withelectrically conductive security features, and such as electroniccircuit units having IC-chip and coil for applications such ascontactless data carriers in the form of flat material, as well as foilcircuit elements which can be formed as a card body of a chip card orcan be integrated in a chip card or in any other flat material.

B. Related Art

The contactless data transmission is increasingly gaining in importance,for example for the purposes of checking and controlling goods, formarking goods of the most different kind in order to avoid forgery ortheft, and in particular also for electronic ID documents. The datacarrier here typically is an IC-chip with antenna. The chip consists ofa plurality of electronic components, and the antenna is an electricallyconductive layer, typically in the form of a coil. The storedinformation can be read-out and displayed for example on a display orcause certain mechanical reactions, for example releasing or blockingthe access to a certain region of a building. It is desirable to keepthe contactless circuit units as small and in particular as flat aspossible so that they can be attached in the form of labels to thesurface of objects or integrated as inlets in the layer construction ofa card, for example of an ID document, or of any other flat object.

Such a circuit unit is known for example from EP 0 756 244 A2. Thedisclosed circuit unit comprises at least one insulating carriersubstrate on which there is located a conducting, flat coil, and anintegrated circuit whose connection points are conductively connectedwith the coil ends directly or via contacts or are capacitively coupledthereto. On the insulating carrier material there are applied coillayers alternately to insulating layers, wherein each insulating layerhas at least one passage through which the adjacent coil layers areconductively interconnected, or wherein the adjacent coil layers arecapacitively coupled, so that the individual coil layers yield a coil.The coil layers are preferably printed on with a conductive lacquer orare sprayed on using a corresponding mask or are etched out of aconducting coating located on the carrier material. Other knownmanufacturing methods are, for example, applying the coil in the form ofan electrically conductive coating through a hot stamping method to thecarrier material, or punching out the coil of a metal foil or anelectrically conductive coated plastic foil and applying it to thecarrier material.

A preferred method for manufacturing coil layers and other conductorstructures is an etch-free screen printing method, wherein a printingpaste with a conducting material is printed on. After the printing, thecarrier material is subjected to a heat treatment, in order to removevolatile components of the printing paste.

It is also often desired to activate or to deactivate, i.e. to switch onand off, electronic functional elements, such as chip modules. For thispurpose, foil switching elements or foil push-buttons are known. Formanufacturing a foil switching element, several foil layers, betweenwhich a switching contact is to be established, are put one on top ofthe other and glued to each other. Here, between two electricallyconductive switching foils (contact foils) there is arranged aperforated and electrically insulating intermediate foil, which servesas a spacer and prevents the contact foils from touching each other inthe resting state of the foil switching element. The intermediate foilthus effects that the foil switching element is open in the restingstate. Through the exertion of pressure on at least one of the twocontact foils in the region of the perforation of the intermediate foil,the contact foil is deformed and an electrical contact is establishedbetween the two contact foils. If no more pressure is exerted, thecontact foil takes on again its original form, as a result of itselasticity. Thereby, the electrical contact between the two contactfoils is interrupted. The foil switching element therefore closes theconductor circuit only during the exertion of a pressure on at least oneof the two contact foils and opens it upon decrease of the pressure.

The contact between the switching foils of the “switch” and theconnection of the switch to the functional elements is establishedthrough electrically conductive conductor structures. These structurescan be produced in the same way as the above-mentioned flat coils, theproduction by printing technology being preferred.

Particularly preferably, for the manufacturing of the conductorstructures, such as conductor paths, conductive areas and contact areas,pastes with metallic particles are employed, for example silverconductive pastes having silver particles, which are printed on thefoils. Here, the problem arises that circuit units and foil switchingelements, which are suitable for the integration into chip cards or forfoil keyboards or other flat objects, normally consist of plastic foils,that is, the conductor structures must be formed on plastic foils,whereby the foils, moreover, often are thin with thicknesses in therange of about 50 μm to 300 μm. Such plastic foils, however, at highertemperatures are susceptible to distorting, curling and in the worstcase shrinking. This property restricts the possibilities of producingflat conductor structures on plastic foils. Structures printed on bymeans of conductive pastes having metallic particles can only be driedat moderate temperatures, in the case of the usual carrier foils, suchas for example PVC and amorphous PVC, at a maximum of 50° C.;polycarbonate, biaxially oriented polyester and paper are suitable fortemperatures of about 100° C. The same applies to paper-based materials,as they are employed for security papers and value documents, forexample for banknotes. Such value documents often have securityfeatures, the check criterion of which is the electrical conductivity.Mostly, it is desired to incorporate the security features ininconspicuous fashion. Manufacturing narrow, flat, inconspicuousconductor structures on or in substrates that are nottemperature-resistant, as they are employed for value documents,however, is practically impossible.

At temperatures applicable to usual plastic foils and paper-based foils,there cannot take place a sintering of the metal particles forming theconductor structures. The result is a poor electrical conductivity incomparison to solid metallic conductor structures and a high metalconsumption, in order to achieve an acceptable conductivity. Since theconductor structures are manufactured preferably with precious metals,such as silver, a high metal consumption simultaneously causes highcosts. Furthermore, relatively high conductor structure thicknesses arerequired. Nevertheless, the achieved electrical conductivities stillneed to be improved. With silver conductive pastes there can be achievedvalues of at best about 1/10 of the conductivity of solid silver,typically much less, about 1/20 of the conductivity of solid silver.

Therefore, there is a need of an improved method for producingelectrical conductor structures on foil materials, in particular forproducing electrical conductor structures for electronic circuit unitsand other elements having electrically conductive conductor structures,which elements are integratable in flat materials, such as chip cards.

SUMMARY OF THE DISCLOSURE

It is therefore the object of the present invention to provide such amethod. The method should offer a combination of as many as possible,preferably all, of the following advantages:

-   -   it should allow the formation of conductor structures on        non-temperature-stable carrier substrates, such as plastic foils        or foil materials;    -   it should allow the formation of conductor structures having a        good electrical conductivity;    -   it should allow the formation of flat conductor structures;    -   the necessary material consumption should be low;    -   the process duration should be short;    -   it should be possible to check the electrical conductivity of        the conductor structures prior to their further processing into        an end product.

It is also an object of the present invention to provide a method formanufacturing a laminate material having electrically conductiveconductor structures, as well as the corresponding foil materials andlaminate materials.

It is furthermore the object of the present invention to provide flatmaterials having such conductor structures, which are equipped or can beequipped with functional elements, such as an IC-chip, and which aresuitable to be integrated into a card construction.

It is moreover the object of the present invention to provide cardshaving such conductor structures and electronic functional elements,such as contactless data carriers.

The central idea of the present invention is to produce electricallyconductive conductor structures by means of so-called “nano-inks”, toproduce these conductor structures, however, not on the final carriermaterial, but on a temperature-stable intermediate carrier, and to thentransfer them onto the final carrier material that does not need to betemperature-stable.

As already mentioned above, chip cards and laminate materials havingelectronic circuit units, which are suitable for the integration intochip cards and other flat materials, for example foil keyboards,typically consist of plastic foils, in particular of hot-laminatableplastic foils. Materials are for example thermoplastics such aspolyesters, polycarbonates, polyolefins, polyamides, fluoropolymers andvinyl polymers, preferably PVC. Upon the formation of electricallyconducting structures on the foils typically employed for the statedpurpose, it is to be taken into account that the foils are nottemperature-stable, that means that in case of a too strong heating theydecompose in the worst case, but at least soften and lose their formthereby. A deformation of the foils having the conductor structures,however, needs to be absolutely avoided, in particular since otherwiseregister problems occur. A comparable problem occurs with foil materialsmade of paper or of paper/plastic mixtures as they are employed forvalue documents, for example banknotes. These foil materials, too,cannot be exposed to high temperatures without changing, for example,curling or decomposing.

A preferred method for manufacturing conductor structures on foils forcard constructions therefore consists at present in applying conductivepastes having metal particles, for example having silver particles, tothe foils in the form of the desired conductor structures by the screenprinting method, then drying the foils at a temperature of no more than50° C., typically in the tunnel drier of the screen printing system, andsubsequently connecting the dried foils having conductor structures intoa laminate material through hot lamination. In the finished conductorstructures of the laminate material the metal particles are present asmutually contacting individual particles. The electrical contact, andthus the electrical conductivity, between mutually contacting individualparticles is considerably worse than it would be the case with acontinuous conductor structure, for example with a conductor structureetched out of a solid metal layer. Hence, in order to achieve areasonably acceptable conductivity, relatively thick conductorstructures must be formed. High material consumption and therefore highcosts are the consequence.

According to the invention, there has now been found a way to achieve,despite the employment of non-temperature-stable carrier materials, asintering of the metal particles of the conductive pastes and thus aconsiderably better conductivity.

According to the invention, as conductive pastes there are employednano-inks. Nano-inks are aqueous suspensions or solvent-basedsuspensions of metallic particles which have particle diameters in therange of some 10 nm, typically 20 nm to 1000 nm. Metallic particles areparticles of pure metals or of metal alloys, preferably silverparticles, aluminum particles and particles of copper-nickel alloys. Thecontent of nanoparticles in the suspensions is for example 10 wt % to 30wt %, the content being primarily determined by the desired applicationmethod. Suitable application methods are in particular printing methods,preferably screen printing, flexographic printing, aerosol printing,inkjet printing and gravure printing. Particularly preferred is a screenprinting method. Here, relatively high particle concentrations can bepresent, for example about 40 to 60 wt % metallic nanoparticles.

Suitable nano-inks are available from Bayer, for example the nanosilverdispersion Bayink TP S, with a silver content of 20 wt %, and thenanosilver and nanoaluminum dispersions of NovaCentrix. The standardnanosilver dispersions have particle diameters of 25 nm or 35 nm.However, dispersions with particle sizes of 10 nm to 100 nm are alsoavailable.

The nanoparticles have the advantageous property that they aresinterable at much lower temperatures than the particles of conventionalconductive pastes. Customary conductive pastes have for example anaverage particle size of 2 μm, but here there are large variances.“Sintering” is understood to mean a superficial baking together of theindividual particles, possibly, with superficial fusing. By the bakingtogether, the electrical contact and thus the electrical conductivity isconsiderably improved compared to merely mutually contacting individualparticles. There arises a quasi transition state between individualparticles merely physically mutually contacting and a conductor path ofsolid material. It holds approximately that the electrical conductivityof the conductor structure is the better the higher the sinteringtemperature of the nanoparticles is.

Silver-nanoparticles sinter at a temperature of about 150° C. Thissintering temperature of the nanoparticles, however, is still much toohigh for conductor structures, which are printed on plastic foils, asthey are employed for laminate materials made of or with hot-laminatablefoils, or on paper, to be able to be exposed to these temperatures. Thefoil materials would be drastically distorted thereby, be curled or evenbe decomposed. The decomposition of commercially availablehot-laminatable foils begins, for example already at 160° C.

According to the invention, the sintering of the nanoparticles istherefore not effected on their final carrier material, but on atemperature-stable intermediate carrier. The method according to theinvention for equipping a foil material with conductor structurestherefore has two basic method steps, namely the production of theconductor structure on a temperature-stable transfer material, on theone hand, and the transfer of the conductor structure onto the desiredfinal carrier material, typically a non-temperature-stable foil, on theother hand, wherein a foil is understood to be flat materials ofarbitrary dimensions, for example in band form or web form, and ofarbitrary composition, typically made of plastics and/or paper. The flatmaterials are usually thin, i.e. they have thicknesses of 500 μm orless, typically 100 μm or less.

“Not temperature-stable” means that the final carrier material would notwithstand the sintering process of the nanoparticles in unchanged form,but would change its shape and/or physical properties and/or chemicalproperties. Whereas a “temperature-stable” material suffers no changesat the minimum temperatures of about 150° C. necessary for thesintering.

For producing the conductor structure or the conductor structures on thetemperature-stable transfer material, there is first applied onto asurface of the transfer material a dispersion containing metallicnanoparticles, in the following referred to as “nano-ink”, in the formof the conductor structure to be formed, but mirror-inverted to thefinal conductor structure, since the transfer process onto the finalcarrier material causes a mirroring of the conductor structure. Theresult is a precursor conductor structure of metallic nanoparticleswhich are mutually touching, at least after the removal of the carriermedium by drying.

The transfer material can have for example the form of an endless band,which is led in a circle and continually re-used, or it can be a bandwhich is unwound from a storage roll and wound onto another storage rollafter it has been used, with or without conductor structure(s), or itcan have the form of a roller or a plate. Forms, which make possible acontinuous conducting of the process, such as bands or rollers, arepreferred.

Suitable transfer materials are materials, to which the nano-inks do notadhere too strongly, because the sintered conductor structures mustagain be stripped off of the transfer material, on the one hand, andwhich are not impaired by the necessary sintering temperatures, on theother hand. The transfer material does not need to be electricallyinsulating, since it is no longer present upon the use of the conductorstructures.

Possible transfer materials are primarily metals, metal alloys and hightemperature-resistant plastics. Suitable metals and metal alloys are forexample preferably steel or aluminum, also metallic or coated withpolymers, in order to produce optimized stripping or transferproperties. Suitable plastics are all those plastics which havelong-term use temperatures of over 150° C. Preferably, the plastics havelong-term use temperatures of at least 200° C., more preferably at least230° C., and particularly preferably 250° C. and higher. Such plasticsare for example some fluoropolymers and polyimides, wherein Kapton(DuPont), which is heatable to 400° C., is especially preferred. Alsoperfluoroalkoxy polymers, which have long-term use temperatures up to260° C., are very suitable.

Also combinations of metals or metal alloys and plastics can be used,for example bands or rollers of metal with a plastic coating or bands orrollers of a different material with a coating of metal or plastic. Manyhigh-temperature-resistant plastics, in particular perfluorinatedpolymers, have the advantage that their adhesion force to othermaterials is low. This means that they have good release properties forthe sintered conductor structures, which facilitates the transferthereof.

The way of application of the nano-inks in principle is arbitrary, butpreferably the nano-inks are printed. The selection of the optimumprinting method primarily depends on the kind of nano-ink to be employedor its content of nanoparticles. Examples of nano-inks and suitableapplication methods have already been mentioned.

The nano-ink is applied in the form which the finished conductorstructure is to have. This conductor structure is formed of theprecursor conductor structure produced by means of the nano-ink, throughsintering.

The sintering of the precursor conductor structure is effected bysupplying heat, i.e. by heating the precursor conductor structure to atemperature which is sufficient for at least partly sintering themetallic nanoparticles.

The temperature must therefore reach at least 150° C., and since thesintering is the better the higher the temperature, it is preferred tosinter at at least 200° C., particularly preferably at at least 230° C.,and in particular at 250° C. or higher. The sintering can be effectedfor example by the transfer band being led through a furnace, or byirradiation with infrared radiation. A sintering by means of laser isalso possible. When employing a roller as a transfer material, primarilyIR sintering or laser sintering come into consideration.

Since with the method according to the invention there can be appliedrelatively high sintering temperatures, the sintering is effected withina short time span, i.e. within 30 seconds, preferably within 15 seconds,particularly preferably within 10 seconds or less. In case ofparticularly high-temperature-resistant transfer materials, such asKapton, sintering times of under 5 seconds can be achieved. The veryshort sintering times bring along an altogether short process duration.

In particular with very high sintering temperatures it can beadvantageous to briefly dry the precursor conductor structure before thesintering process, i.e. to remove the dispersion medium. The drying canbe effected on the way to the sinter station for example byIR-treatment, whereby the radiated energy is to be suitably determinedso as to avoid a damage to the precursor conductor structure by asuddenly starting evaporation of the dispersion medium.

After the sintering of the metallic nanoparticles forming the precursorconductor structure, now an excellently electrically conductiveconductor structure is present on the surface of the transfer material.In a next step, this conductor structure is transferred onto the finalcarrier material. Since the final carrier materials are preferablyhot-laminatable foils which are not temperature-stable, the transfermaterial having the conductor structures thereon is cooled down to atemperature which is compatible with the temperature resistance of thefinal carrier material, before it is brought in contact with the finalcarrier material. Preferably, cooling down is effected to a temperatureof 50° C. or below. The cooling down can be effected simply by thetransfer material having to run through a sufficiently long path lengthbetween sinter station and transfer station, or it can be supported byequipment, for example by a slight airflow.

The conductor structures produced in this way on the transfer materialhave, due to the sintering of the nanoparticles, a very good electricalconductivity, which lies approximately in the range of 20% to 50% of theconductivity of the corresponding solid material. The conductorstructures can therefore be very flat, that is, have thicknesses in therange of about 1 to 25 μm, preferably of about 2 to 10 μm.

The conductor structures are now transferred from the temperature-stabletransfer material, which may or may not be electrically insulating, tothe final, electrically insulating carrier material. Electricallyinsulating means in this context that the electrical conductivity of thefinal carrier material is negligibly low in comparison to the conductorstructures. The ratio of the conductances of the conductor structures tothe conductances of the electrically insulating carrier foils should beabout 1:1,000,000, preferably 1:1,000,000,000. The final carriermaterials, of course, can also be temperature-stable, but normally themethod of the invention for attaching conductor structures tonon-temperature-stable foil materials will be employed, for example, forattaching conductor structures to the hot-laminatable foil materialsfavored for manufacturing laminate materials for chip cards, such aspolyester foils, polycarbonate foils, polyolefin foils, polyamide foilsand other thermoplastic foils. A foil material particularly preferred asa final carrier material is PVC.

The transfer of the conductor structures from the transfer material ontothe final foil material can be effected immediately after themanufacturing of the conductor structures and, where applicable, thecooling down of the transfer material. When the transfer material is aroller or is located on a roller in the form of a coating, clothing,etc, an instantaneous transfer is the only expedient possibility. Incase of a transfer material in band form or web form or in the form ofindividual transfer material sheets it is also possible, however, toperform the transfer at a later point in time. The transfer materialwith the conductor structures formed thereon is then wound or stackedand can be temporarily stored and/or transported. It constitutes anintermediate product in the manufacture of a foil material havingelectrically conductive conductor structures.

For transferring an electrically conductive conductor structure from thetransfer material onto the final carrier foil, the transfer material andthe final carrier foil are brought together such that the conductorstructure to be transferred is located between mutually touchingsurfaces of transfer material and final carrier foil. By exerting apressure on the layer of transfer material/conductor structure/foilmaterial, the conductor structure is transferred from the transfermaterial onto the foil material, as it has a greater adhesive force tothe foil material than to the transfer material. This difference in theconductor structures' adhesive force to the transfer material, on theone hand, and to the foil material, on the other hand, is decisive for asuccessful transfer of the conductor structures. Therefore, there arepreferably taken measures, in order to achieve as great a difference inthe adhesive forces as possible. Such a measure is to wash off thetransfer material with a surfactant solution before use, or to equip itwith a release coating. Such release coatings are known. Suitable arefor example Teflon and silicone coatings or certain nanoparticlecoatings. Here it is decisive that the surface tension of the substratestill permits a sufficient wettability through the nano-ink. Anotherpossibility is to pretreat or to coat the final foil material inadhesion-enhancing fashion. An adhesion-enhancing pretreatment is forexample a corona treatment, and an adhesion-enhancing coating is acoating with an adhesive. Suitable adhesives are in particular adhesivesactivatable by pressure and/or heat, which without activation aretack-free. Tack-free means in this context that the foil material havingthe adhesive coating can be rolled or stacked and stored withoutsticking together. Suitable adhesives are for example polyamides,polyurethanes or combinations thereof, which for a thermo-activatabilityare covered with protective groups. The measures can be appliedindividually or in combination.

A further possibility to promote the transfer of the electricallyconductive conductor structures from the transfer material onto thefinal foil material is to heat the foil material. Heated thermoplasticfoils exert a greater adhesive force on the conductor structures thannon-heated foils, and a slight heating of the foil material is oftenalready sufficient in order to ensure a satisfactory transfer of theconductor structures. Of course, the heating must not be so strong thatthe foil material would be impaired thereby, i.e. would distort or evendecompose. Since the foil material in the moment of the transfer isspatially fixed, it is relatively temperature-tolerant. A heating to 50,60 or 70° C. is usually not a problem.

A particularly good adhesion to the foil material can also be achievedby means of special nano-inks which have a proportion of adhesive-likematerials. Suitable are for example nano-inks having an acrylate epoxymatrix.

The transfer can be effected in principle in every device which issuitable for exerting pressure on the materials brought together and,where applicable, for supplying heat to these. For example a press wouldcome into consideration, where applicable, with heatable plates, butpreferably the transfer is carried out between two rollers, which makespossible a continuous conducting of the process. If during the transferalso a heating is to be performed, it is preferred to realize one orboth rollers, in particular the roller at the side of the final foilmaterial, in heatable fashion. When the transfer material is formed as aroller, the transfer material itself represents one of the two rollers,through which the foil material is led for transferring the conductorstructures. If the transfer material is a band or a web, i.e. a “wide”band, on which several conductor structures can be formed side by side,the transfer material and the final foil material are brought togetherin a separate transfer device. This transfer device consists preferablyof roller and counterpressure roller.

The final foil material has preferably the form of bands, webs orsheets. It should, of course, be at least so wide that all the conductorstructures formed on the transfer material, where applicable, conductorstructures formed side by side, can be completely transmitted.

After the transfer of the conductor structures onto the final carriermaterial, the single copies of the desired size are detached therefrom.Although it is in principle also possible to manufacture each of thesingle copies individually, this way of manufacturing is less preferreddue to its cumbersomeness and elaborateness. It is particularlypreferred to employ a band-shaped or web-shaped transfer material, sincesuch a transfer material offers the greatest freedom in conducting theprocess. In particular, the path lengths which are required for thesintering and, where applicable, for a predrying before the sinteringand/or for a cool down after the sintering, can be freely selected heredepending on the requirements. In addition, it is possible to decouplethe two main method steps of the method of the invention from eachother, namely the manufacturing of the conductor structures on thetransfer material, on the one hand, and the transfer of the conductorstructures onto the final foil material, on the other hand. The transferof the conductor structures from the transfer material onto the finalfoil material can be effected temporally and locally independently ofthe manufacturing of the conductor structures on the transfer material.

The foils equipped with conductor structures or with at least oneconductor structure can now be combined with further foils, whichlikewise have, where applicable, one or several conductor structures,into a laminate material. Some exemplary embodiments of laminatematerials according to the invention are represented in FIGS. 4 to 9.The preferred lamination method is hot lamination. Preferably, formanufacturing the foil composite of the laminate material, exclusivelyhot-laminatable foils are employed, but foils which are nothot-laminatable can in principle also be employed as well. When thefoils have a too high softening point for the hot lamination processcarried out, there must be provided between the corresponding foil andthe adjacent foil or the adjacent foils a suitable adhesive, such as ahot-melt adhesive, so that, as with hot lamination, a connection inmaterial-locking fashion is produced between the foils. Preferably, ascover layers of the foil composite material, foils are laminated on orlined on which serve as protective layers, improve the moistureresistance, or are electrostatically chargeable. The laminated-on orlined-on foils can also be populated with electronic components or otherelements. All materials can be, as desired, light-transmissive or opaqueand, where applicable, colored. It is evident that all foils which arein contact with conductor structures must be electrically insulating.The individual foils can extend in each case all-over the entirelaminate material, but it is also sufficient when they have suitabledimensions so as to separate adjacent conductor structures in aninsulating fashion. This means that with the method according to theinvention for equipping a foil material with conductor structures, thisfoil material not necessarily must be formed all-over, but in many casesalready has the through openings desired in the later laminatematerials.

The lamination is preferably effected between lamination plates of alaminating press at a temperature, depending on materials, of about 100°C. to 150° C., but for example can also be carried out between twolamination rollers. The lamination can be carried out with laminatematerials having the desired final dimensions, but preferably sheetmaterials having a multitude of single copies, which are later cut tothe desired dimensions, are laminated to each other. The foil materialhaving conductor structures obtained according to the method of theinvention, which is preferably manufactured in band form or web form,accordingly is cut, for lamination, to the desired sheet materialdimensions. The lamination can be performed in such a way that all thefoils of the laminate material to be manufactured are laminated in onesingle working process into a foil composite, or that two or morepartial foil composite materials are manufactured which then arelaminated or lined to each other in a further working process into thedesired laminate material.

The obtained laminate materials can be already finished cards, buttypically are inlets which are to be integrated into a cardconstruction. When an inlet has the same dimensions as the card itself,it extends over the entire surface of the card, and in the cardconstruction there do not occur thickness variations. It is thereforepreferred to manufacture the laminate materials of the invention in thedimensions of the card or of the other flat material element into whichthey are to be integrated.

The laminate materials having conductor structures, according to theinvention, can be combined in a per se known manner with electronicfunctional elements and then form for example electronic circuit unitsfor the contactless data transmission or foil keyboards. In particular,there can be manufactured conductor structures in one or in severallayers, which act as antennas in a circuit unit for the contactless datatransmission, or which form a switch and switch on or off electronicfunctional elements in the same or in different levels of a laminatematerial.

The construction of such circuit units is per se conventional withregard to materials (of course, apart from employing nano-inks andequipping the foil material with conductor structures by means oftransfer method), with regard to the required layer constructions, whereapplicable with regard to a through-contacting between the layers, andwith regard to the connection with electronic functional elements. Inthis context, particular reference is made to the European patentapplication 0 756 244 A2.

DESCRIPTION OF THE DRAWINGS

The invention will hereinafter be illustrated further on the basis ofFigures. It is pointed out that the Figures are not true to scale andnot true to proportion. Further, the features represented in a Figureare not only applicable in combination with the other featuresrepresented in the corresponding Figure. Rather, features described inthe context of a particular embodiment can be applied in general withthe laminate material according to the invention. The same referencenumbers designate the same or corresponding elements. There are shown:

FIG. 1 a laminate material according to the invention in a top view,

FIG. 2 a schematic representation of an embodiment of a device forcarrying out the method according to the invention for equipping a foilmaterial with at least one electrically conductive conductor structure,

FIG. 3 a schematic representation of a different embodiment of a devicefor carrying out the method according to the invention for equipping afoil material with at least one electrically conductive conductorstructure,

FIG. 4 a chip card according to the invention in a top view,

FIG. 5 the chip card of FIG. 4 in a perspective view,

FIG. 6 a cross-section along the line A-A of FIG. 5,

FIG. 7 a partial sectional view of a laminate material according to theinvention with a switch in an exploded view,

FIG. 8a, 9a respectively top views from below onto a conductor structureof the switch of FIG. 7, and

FIG. 8b, 9b respectively top views from above onto conductor structuresof the switch of FIG. 7 opposing the conductor structure of FIG. 8a , 9a.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows a laminate material 11 according to the invention in a topview. The laminate material 11 has a layer made of a first foil material2, i.e. a first foil layer 2, and a layer made of a second foilmaterial, i.e. a second foil layer. The second foil layer is transparentand therefore not recognizable in the Figure, so that a first conductorstructure 5 and a second conductor structure 6 are visible between thefoil layers. The conductor structure 5 is connected with the conductorstructure 6, for example the conductor structure 6 is connected with theleft end of the conductor structure 5. The ends of the conductorstructures 5, 6 for connection with an electronic functional element,such as an IC-chip, are respectively shown in a broadened fashion. TheIC-chips themselves are omitted in the schematic representation. Thefirst conductor structure 5 is a conductor path in the form of a coil,as is required for data carriers for the contactless data exchange orfor the contactless energy supply. For manufacturing the laminatematerial 11, a nano-ink, for example a suspension having silvernanoparticles, is printed onto a surface of a transfer material, forexample by screen printing method or by flexographic printing method.The nano-ink is respectively applied in a shape corresponding to theshape of the desired conductor structures 5, 6. In so doing, precursorconductor structures are formed which consist of individualnanoparticles. The transfer material having the precursor conductorstructures is now dried, preferably by leaving the nano-ink's carriermedium to evaporate during the transport of the transfer material havingthe precursor conductor structures to the sinter station.

In the sinter station, for example a tunnel furnace through which thetransfer material is led, the silver nanoparticles are subjected to asintering process at a temperature of for example 250° C. In so doing,from the first precursor conductor structure there results the firstconductor structure 5 and from the second precursor conductor structurethere results the second conductor structure 6. Subsequently, thetransfer material having the conductor structures 5, 6 is left to cooldown and then it is brought together with the first foil material 2. Thebringing together is effected for example in the roller nip of tworollers forming a transfer station. In the roller nip, the conductorstructures 5, 6 are transferred from the transfer material onto thefirst foil material 2. The first foil material 2 is then covered with asecond foil material on the surface on which now the conductorstructures 5, 6 are located, and the two foil materials are laminatedinto the laminate material 11. In the foil material 11 the conductorstructures 5, 6 are enclosed in protected fashion between the first foillayer 2 made of the first foil material and the second foil layer madeof the second foil material.

FIG. 2 illustrates the carrying out of the method according to theinvention. A transfer material band 30 with a surface 31 is led in acircle by transport rolls 32, 33 which are driven by a not shown drive.The transport material band consists for example of ahigh-temperature-resistant plastic such as Kapton. The arrows in therolls 32, 33 state the sense of rotation of the rolls. A flexographicprinting unit 21 is schematically indicated by a printing cylinder 22with printing plates, a nano-ink transfer roller 23 and acounterpressure roller 24. By means of the printing unit 21 precursorconductor structures 20 are printed onto the surface 31 of the transfermaterial band 30. The precursor conductor structures 20 are printed inthe form and arrangement in which they are to be present later on thefinal carrier material, however, mirror-inverted, since the transferprocess onto the final carrier material causes a mirroring of thestructures. In FIG. 2, the precursor conductor structures 20 areschematically drawn as rectangles, however, the structures of course canhave any forms. There can also be arranged several precursor conductorstructures 20 side by side, which requires an accordingly greater widthof the transfer material band 30, i.e. a transfer material web.

The transfer material 30 is continuously transported in the direction ofthe arrow, whereby the precursor conductor structures 20 reach a sinterstation 28. The sinter station 28 is for example a tunnel furnacethrough which the transfer material band is led, or an IR radiator oranother heat source. Before reaching the sinter station 28 the precursorconductor structures 20 consist of metallic nanoparticles in a carriermedium, the carrier medium evaporating to a more or less strong extenton the transport path between printing unit 21 and sinter station 28. Ifa complete evaporation is desired, a sufficiently long transport pathcan be ensured, for example by a meandering guidance of the path of thetransfer material band 30 or by an additional heat source betweenprinting unit 21 and sinter station 28. In the sinter station 28 theprecursor conductor structures 20 are heated to a temperature which issufficient for the sintering of the metallic nanoparticles. Preferably,the upper limit of the long-term use temperature of the transfermaterial is selected to be the sintering temperature, since thesintering and thus the conductivity of the final conductor structures isthe better the higher the sintering temperatures are. Furthermore, thesintering time is the shorter the higher the sintering temperature is.In the case of silver nanoparticles and a sintering temperature of about250° C., the sintering process lasts only a few seconds. After thesintering there are no longer present metallic nanoparticles whichmutually contact merely physically, as in the precursor conductorstructures 20, but there have been formed continuous metallic structureswith correspondingly good conductivity.

These “finished” conductor structures 5 are now transported further, inorder to be transferred onto their final carrier material. The finalcarrier material 2, for example a PVC foil, is not temperature-stable,which is why the transfer material band 30 having the conductorstructures 5 must be sufficiently cooled down before the contact withthe final carrier material 2. Cooling down is effected automatically onthe transport path or by a (not shown) cooling device between the sinterstation 28 and the transfer station 40. In the represented embodiment,the transfer station 40 consists of the transport roll 33 of thetransfer material band 30 and a counterpressure roller 43. The foilmaterial 2, onto the surface 2′ of which the conductor structures 5 areto be transferred, is located on a storage roll 41, is unwound from thisstorage roll and led through the roller nip of the transfer station 40,and is finally again wound onto a further roll 42. The arrowsrespectively indicate the movement directions. The foil material 2expediently has about the same width as the transfer material band 30,in the represented embodiment a width which does not allow aside-by-side arrangement of precursor conductor structures 20 orconductor structures 5. The foil material 2 is represented as acontinuous foil, but the foil material can also have through openingsdepending on the later purpose of use.

The transfer material band 30 having the conductor structures 5 on itssurface 31 and the foil material 2 are contacted with each other in theroller nip of the transfer station 40 such that the conductor structures5 touch the surface 2′ of the foil material 2. Through the pressureexerted in the roller nip, they are pressed onto the surface 2′ andremain adhered thereto. This adhesion is supported by a heatedcounterpressure roller 43, which slightly heats the foil material 2, forexample to a temperature of about 50° C., and thus gives to the surface2′ a greater adhesive force. When the foil material 2 and the transfermaterial band 30 are again separated from each after leaving the rollernip, the conductor structures 5 are located on the surface 2′ of the PVCfoil, while the transfer material band 30 is again free of conductorstructures and can anew be printed with precursor conductor structures20. The PVC foil 2 equipped with conductor structures 5 is wound ontothe storage roll 42 or, alternatively, immediately after the equipmentwith conductor structures 5 cut into segments having dimensions, as theyare suitable for the later lamination into a laminate material.

In the embodiment represented in FIG. 2, the transfer material 30 hasthe form of an endless band, which causes that the manufacturing of theconductor structures 5 on the transfer material 30 and their transferonto the foil material 2 expediently must be carried out in directsuccession, i.e. in a combined system. Alternatively, it is alsopossible, however, to feed the transfer material band 30, similar to thefoil material 2, from a storage roll, to form thereon the conductorstructures 5, and to then again wind the transfer material band equippedwith the conductor structures 5 onto a storage roll, in order to employit for transferring the conductor structures 5 onto a foil material 2only at a later point in time and in another system. In such anembodiment the transfer material band 30 would be fed to the transportroll 32 by a transfer-material storage-roll, and instead of or after thetransport roll 33 there would be a further storage roll, onto which thetransfer material band having the finished conductor structures 5 wouldbe wound.

The foil material 2 can be equipped with conductor structures also onits two surfaces. For this purpose, for example the counterpressureroller 43 could be replaced by a further arrangement of transfermaterial, printing unit and sinter station.

FIG. 3 shows an alternative embodiment of the transfer material. In theembodiment represented in FIG. 3, the transfer material has the form ofa roller 35 with a surface 36 on which the precursor conductorstructures 20 are printed. The roller 35 can consist for example ofmetal or of a high-temperature-resistant plastic, such as Kapton, orthere can also be employed a metal roller which is coated with a hightemperature-resistant plastic. The transfer material roller is rotatedby means of a not shown drive. Instead of the flexographic printing unit21 of FIG. 2, in the embodiment of FIG. 3 there is employed an inkjetprinter, which is schematically indicated as a printhead 25. Theemployment of a roller-shaped transfer material allows less degrees offreedom in carrying out the method than the employment of a band-shapedor web-shaped transfer material. As it is directly apparent from FIG. 3,the transfer material roller 35 forms a part of the transfer station 40(together with the counterpressure roller 43), so that it is notpossible to temporally and locally decouple the manufacturing of theconductor structures 5 and their transfer onto the foil material 2. Inaddition, the transport paths between printer 25 and sinter station 28,as well as between sinter station 28 and transfer station 40 are definedby the circumference of the roller 35. As heat source for sinteringsubstantially a radiation source comes into consideration. Otherwise,the embodiment represented in FIG. 3 corresponds to the embodimentrepresented in FIG. 2.

The FIGS. 4 and 5 show a chip card 1 in a top view and in a perspectiveview. The chip card 1 also has a coil, like the coil of FIG. 1 formed bythe first conductor structure 5. The coil 13 of the chip card 1,however, consists of two coil layers which are separated by aninsulating foil layer. The chip card 1 has a layer made of a first foilmaterial 2, i.e. a first foil layer 2, a layer made of a second foilmaterial 3, i.e. a second foil layer 3, and a layer made of a third foilmaterial, i.e. a third foil layer, which is not represented in FIGS. 4and 5. The foil layers each are electrically insulating plastic foils.Between the first foil layer 2 and the second foil layer 3 there islocated the first conductor structure 5 which forms a first coil layer,and between the second foil layer 3 and the third foil layer there islocated a second conductor structure 6 which forms a second coil layer.The second foil layer 3 has through openings 15, 16. The opening 16serves to interconnect the first conductor structure 5 and the secondconductor structure 6 in an electrically conductive fashion, asexplained in more detail in FIG. 6. Therefrom results the “two-layer”coil 13. The contact window 16 in the intermediate layer 3, however, canalso be omitted. Then, between the two coil layers there exists noelectrically conductive connection. Instead, the coil layers arecapacitively coupled.

The through opening 15 in the central region of the foil layer 3 servesto establish an electrically conductive connection between the ends 8, 9of the coil 13 and an IC-chip 12. In particular, the end 8 of the firstconductor structure 5 is located on the first foil layer 2, and it wouldbe covered with a foil layer 3 without through opening 15. In therepresented embodiment, the dimensions of the second foil layer or ofthe intermediate layer 3 are chosen such that the second foil layer 3merely insulates the first conductor structure 5 from the secondconductor structure 6, but does not cover the central region of thefirst foil layer 2. In the represented embodiment, the IC-chip 12 isaccordingly located on a surface of the first foil layer 2. It isconnected with the first conductor structure end 8 and the secondconductor structure end 9 via bonding wires 18 in a per se known manner.Alternatively, however, also the second foil layer 3 can be formedall-over. In this case, also the integrated circuit 12 is capacitivelycoupled to the coil 13, analogous to the capacitive coupling of thefirst and of the second coil layer in the case of the absence of thecontact window 16.

The manufacturing of the chip card 1 is effected by equipping the firstfoil material 2 with the first conductor structure 5 in accordance withthe above-described sinter/transfer method of the invention, equippingthe second foil material 3 or the third foil material with the secondconductor structure 6 in accordance with the above-describedsinter/transfer method of the invention, stacking the foil materials insuch a way that the first conductor structure 5 is located between thefirst foil material 2 and the second foil material 3 and the secondconductor structure 6 is located between the second foil material 3 andthe third foil material, and hot-laminating the foil stack into the chipcard 1.

When the second conductor structure 6 is located on the second foilmaterial 3, a contact window 16 cannot be provided, and the coil layersare capacitively coupled. When the second conductor structure 6 islocated on the third foil material, the second foil material 3 can havethe contact window 16, and between the conductor structures 5, 6 therecan be formed an electrically conductive connection, as represented inFIG. 6.

FIG. 6 shows a cross-section along the line A-A of FIG. 5. Thecross-section illustrates the layer construction of the chip card andthe electrically conductive connection between the coil layers 5, 6through the contact window 16 of the intermediate layer 3. The coillayers 5, 6 overlap each other in the region of the contact window 16,and upon stacking the first foil material 2, the second foil material 3and the third foil material 4, in order to laminate the layers into thelaminate material 11, a small quantity of conductive adhesive 19 isapplied in the region of the contact window 16 to one of the coil layers5, 6. Upon lamination, the conductive adhesive 19 flows into the contactwindow 16 and establishes an electrically conductive connection betweenthe conductor structures 5, 6.

The represented chip card 1 has merely three foil layers. But, ofcourse, there can also be laminated on or lined on further foil layers,whereby these further foil layers can also have electrically conductiveconductor structures, which are manufactured in accordance with theabove-described sinter/transfer method of the invention or in accordancewith another method. These further foil layers can be hot-laminatedsimultaneously with the remaining foil layers, or the hot lamination canbe carried out in several steps, i.e with partial foil stacks.

The represented laminate materials having conductor structures ofsintered metallic nanoparticles, combined with an electronic functionalelement or several electronic functional elements, typically areintegrated as inlets into the layer construction of a card.Alternatively, already the final card construction can be manufacturedin the manner stated herein by equipping foil material with conductorstructures and subsequently laminating the foil materials.

FIG. 7 shows a partial sectional view of a laminate material 11according to the invention with a switch 14. The foil layers arerepresented in the state before the lamination, but in the requiredlayer sequence and orientation to each other. The laminate material 11has a first foil layer 2, a second foil layer 3 and a third foil layer 4as well as further foil layers 10, 10′. On a surface of the foil layer 2there is located a first conductor structure 5 manufactured by means ofthe sinter/transfer method of the invention. On a surface of the foillayer 4 there is located a further conductor structure also manufacturedby means of the sinter/transfer method of the invention, which conductorstructure can have different shapes, as shown in FIG. 8a and FIG. 9a .FIG. 8a shows a conductor structure 7 in the form of a conductive areawithout any connection to other conductor structures, and FIG. 9a showsa conductor structure 6 which is a combination of conductive area andconductor path. In FIG. 7, the conductor structure 7 is represented incontinuous lines, while the conductor structure 6 is represented bydashed lines as an extension of the conductor structure 7.

The FIGS. 8a and 9a respectively show top views from below onto theconductor structures 7 and 6. The FIGS. 8b and 9b respectively show topviews from above onto the conductor structures opposing the conductorstructures 7 and 6, which are located on a surface of the foil 2. In theFIGS. 8b, 9b there is respectively also represented the intermediatelayer 3 which separates the conductor structures on the foils 2 and 4,the “contact foils”, from each other, but has a through opening 17through which the opposing conductor structures can come in contact witheach other. The contact is established through exerting a pressure onthe elastic contact foils of the laminate material 11 in the region ofthe through opening 17 (of the switch window 17), and interruptedthrough terminating the pressure. When no more pressure is exerted, theelastic foils return to their initial states. With this arrangement,electronic functional elements can be switched on and off. The conductorstructures are designed differently, depending on whether a contactbetween different levels of the laminate material is to be establishedor interrupted, or whether a contact in the same level is to beestablished or interrupted.

FIG. 8 relates to the establishing/interruption of an electrical contactbetween conductor structures in the same level. A first conductorstructure 5 and a second conductor structure 6 (FIG. 8b ) can beelectrically conductively interconnected by means of a third conductorstructure 7 (FIG. 8a ).

FIG. 9 relates to the establishing/interruption of an electrical contactbetween conductor structures in different levels. A first conductorstructure 5 (FIG. 9b ) can be electrically conductively connected with asecond conductor structure 6 (FIG. 9a ). The conductor structures 5, 6and 7 (FIG. 8) and the conductor structures 5 and 6 (FIG. 9)respectively form together a switch 14. The manufacturing of such alaminate material 11 having a switch 14 is again effected by equippingfoil material 2 and 4 with the corresponding conductor structures 5, 6and 7 (FIG. 8) or with the conductor structures 5 and 6 (FIG. 9) inaccordance with the sinter/transfer method of the invention, stackingthe foil materials 2 and 4 equipped with the conductor structures aswell as further foil materials 3, 10 and 10′, in the order andorientation to each other as represented in FIG. 7, into a foil stack,and then hot-laminating the foil stack so as to form the laminatematerial 11.

Laminate materials, such as the one shown in FIG. 7, are suitable forexample for manufacturing foil keyboards.

Of course, there can also be combined several functions in the laminatematerials. For example, conductor paths of most different forms, one- ormulti-layered coils, and switches can be contained in one and the samelaminate material. The conductor structures produced according to theinvention by means of nano-inks in the sinter/transfer method aresuitable very well for contacting IC-chips, as they show very lowcontact resistances on usual bonding pads made of gold or platinum.Conductor structures in different levels of a laminate material can bemanufactured with the help of the same or of different nano-inks.

The particular advantages of the conductor structures manufactured fromnano-inks in the sinter/transfer method according to the invention,compared to unsintered conductor structures made of the same nano-ink,include in particular

-   -   a utilization of the metallic material improved by up to 50%        regarding conductivity,    -   a reduction in the thickness of the conductor structures of up        to 50%, which results in advantages in the optical appearance of        chip cards, and furthermore makes possible an inconspicuous        accommodation of electrically conductive structures in value        documents,    -   a reduction of the process duration by a factor of about 10, and    -   an optimal checkability of the electrical properties of the        conductor structures, in particular coils, before the further        processing, in particular before the chip insertion.

The invention claimed is:
 1. A chip card or chip card inlet, comprisinga plurality of foil layers connected through hot lamination and anelectronic circuit unit with at least one 1C-chip and at least one coiland/or at least one foil switch, wherein the conductor structure of thecoil and/or of the foil switch consists of sintered metallicnanoparticles and is obtained by: (a) applying a dispersion, containingmetallic nanoparticles, in a form which corresponds to the form of theconductor structure to be formed, to a surface of a transfer material toprovide a precursor conductor structure formed by the nanoparticles; (b)sintering the metallic nanoparticles forming the precursor conductorstructure by supplying heat to the nanoparticles so as to form theelectrically conductive conductor structure on the surface of thetransfer material; (c) bringing into contact a surface of a foilmaterial and the surface of the transfer material on which theelectrically conductive conductor structure is located; (d) transferringthe electrically conductive conductor structure from the surface of thetransfer material onto the contacting surface of the foil material byexerting pressure; and (e) where applicable, detaching segments of adesired size from the foil material, a segment having at least oneelectrically conductive conductor structure; wherein the steps (c), (d)and, where applicable, (e) are carried out immediately subsequent to thesteps (a) and (b) or at any later point in time, and wherein thetransfer material comprises a heated roller made of or coated with ahigh-temperature-resistant plastic.
 2. The chip card according to claim1, wherein the dispersion containing nanoparticles is an aqueousdispersion or a solvent-based dispersion with a content of nanoparticlesof 10 wt % to 30 wt % and/or with an average particle diameter of thenanoparticles of 20 nm to 1000 nm, wherein the nanoparticles areparticles of pure metals or of metal alloys.
 3. The chip card accordingto claim 1, wherein the application of the dispersion containingmetallic nanoparticles is effected by a printing method.
 4. The chipcard according to claim 1, wherein the sintering of the nanoparticlesforming the precursor conductor structure into the electricallyconductive conductor structure is effected at a temperature of at least150° C., and within a time of no more than 30 seconds.
 5. The chip cardaccording to claim 1, wherein as the foil material to be provided withthe conductor structures there is employed a hot-laminatable foilmaterial.
 6. The chip card according to claim 1, wherein the foilmaterial's surface to be provided with the electrically conductiveconductor structure is pretreated in adhesion-enhancing fashion orcoated in adhesion-enhancing fashion to improve the adhesion to theconductor structure and/or the surface of the transfer material ispretreated or coated in adhesion-reducing fashion to reduce the adhesionto the electrically conductive conductor structure.
 7. The chip cardaccording to claim 1, comprising a contactless data carrier.
 8. The chipcard according to claim 1, wherein the foil material's surface to beprovided with the electrically conductive conductor structure is heatedto improve the adhesion of the foil material to the conductor structure.9. The chip card according to claim 1, wherein the dispersion containingnanoparticles further comprises adhesive materials.
 10. The chip cardaccording to claim 1, wherein the precursor conductor structure formedby nanoparticles on the transfer material is mirror inverted to theelectrically conductive conductor structure formed on the foil material.11. The chip card according to claim 1, wherein the sintering of thenanoparticles forming the precursor conductor structure into theelectrically conductive conductor structure is effected at a temperatureof at least 250° C., and within a time of no more than 5 seconds.